Edits to Excerpts do not qualify you for the Research Assistant Badge.
Retagging a question does not qualify you for the Editor badge.
It looks like you may qualify for the Organizer badge though, maybe. The actual 'retagging' ability isn't actually available to you until 500 rep, but now that anyone can put in a suggested edit that doesn't matter as much. ...
The question list shows you the user who most-recently answered the question or edited a post in the thread.
In both of these cases, however, the users modification (an answer) was subsequently deleted. If you have the reputation to see deleted posts, it would be somewhat more obvious.
It's just a quirk of the software, not (as far as I know) a bug.
This is the expected, correct behavior.
One of the roles of the Community user (which is not a real person) is to periodically bump old questions that are considered "unanswered" so that they get visibility.
It does this without actually editing the question in any material fashion. The bump doesn't even show in the question's timeline. I'm not sure, not ...
That old edits make questions come up in the reopen queue is by design. If a question has been edited after being closed, it is now eligible for reopening.
In regards to questions showing up multiple times - this has been fixed.
1st) There's a shortcut to the FAQ: [faq] and an extended one to the different topics: [faq#TOPIC], where TOPIC is the id/name of the headline/anchor.
Example: Link to the [faq]
Example: Link to the "What kind of questions can I ask here" [faq#questions]
Note: This doesn't work in questions/answers, but in comments and in chat.
2nd) I also have a Gist ...